Simplify. Remove all perfect squares from inside the square roots. Assume $x$ and $z$ are positive. $\sqrt{72x^3z^3}=$
$\begin{aligned} \sqrt{72x^3z^3}&=\sqrt{6^2 \cdot x^2\cdot z^2\cdot 2xz} \\\\ &=\sqrt{6^2}\cdot\sqrt{x^2}\cdot\sqrt{z^2}\cdot\sqrt{2xz} \\\\ &=6\cdot x\cdot z\cdot\sqrt{2xz} \\\\ &=6xz\sqrt{2xz} \end{aligned}$ In conclusion, $\sqrt{72x^3z^3}=6xz\sqrt{2xz}$